This invention relates to punching machines for use with replaceable tools, and particularly to a hand-held, power-driven punching machine suitable for perforating sheet-metal work at sites of construction, among other applications. More particularly, the invention deals with improvements in or relating to a chuck for detachably mounting a punch or other tool to the punching machine.
Conventionally, for chucking a tool to the plunger or ram of punching machines or punch presses, it has been known to employ a set of locking balls slidably received one in each of several ball guideways extending radially outwardly from a tool socket which is cut centrally in one end of the plunger or ram. The tool socket is to have the shank of the tool inserted therein. Concentrically fitted over the plunger, a cam ring is movable axially thereof in sliding engagement with the locking balls protruding partly from the ball guideways, for forcing the balls into an annular groove in the tool shank. The tool is firmly coupled to the plunger in coaxial relationship thereto as all the locking balls are cammed into locking engagement in the groove in the tool shank.
An objection to this familiar tool chuck is that the locking balls as heretofore made have each been truly spherical in shape. The spherical locking balls have rendered the axial dimension of the plunger unnecessarily long for given diameters of the plunger and the tool shank. In hand-held, power-driven punching machines of the kind under consideration, the distance is narrowly limited between the punch in its normal, retracted position and the die. The unnecessarily long plunger has therefore resulted in an unnecessarily long dimension of the machine itself in the axial direction of the plunger.
A known solution to this inconvenience has been the use of screw-type chucks. This alternative type of chucks has, however, a serious drawback of rather readily loosening in use, as the impact of punching is repeatedly exerted thereon. The screw threads of the loose chucks have been easy to be irrecoverably destroyed.
The present invention seeks, in a tool chuck for a punching machine of the kind defined, to make the axial dimension of the chuck less than heretofore for given diameters of the plunger and the tool shank, by making use of preexisting parts only and without in any way adversely affecting the performance or handling of the machine.
Briefly, the present invention may be summarized as a chuck for detachably mounting a tool to a punching machine. Included is a plunger reciprocable axially thereof, the plunger having a tool socket formed in one end thereof for receiving the shank of a tool, and a plurality of ball guideways extending axially outwardly from the tool socket. Locking balls are slidably received one in each ball guideway for movement into and out of locking engagement in an annular groove in the tool shank received in the tool socket. Each locking ball is elongated radially of the plunger, or longitudinally of one ball guideway in which it is received. A cam ring is concentrically mounted on the plunger and movable axially thereof for urging the locking balls into locking engagement in the annular groove in the tool shank.
The invention particularly features the fact that the locking balls are each elongated radially of the plunger, which is tantamount to saying that the locking balls are compressed axially of the plunger. Therefore, for given diameters of the plunger and the tool shank, the dimension of the machine in the axial direction of the plunger can be made correspondingly less than if the balls were truly spherical as in the prior art. Despite the improved shape of the locking balls, moreover, the tool chuck has its field-proven performance intact, permitting the tool to be readily mounted to, and dismounted from, the punching machine, and positively holding the tool in the face of the impact of punching operations.
The present invention further features the fact that the plunger is adapted for easy withdrawal of the tool shank from the tool socket in the event of accidental deformation of the tool shank in the tool socket. For such tool shank withdrawal, the plunger is formed to include an annular enlargement of the tool socket between the ball guideways and one end of the plunger for ease of withdrawal of the tool shank from the tool socket in one embodiment of the invention. In another embodiment the plunger has a plurality of escape passageways which are open to the tool socket and which extend one between each ball guideway and one end of the plunger for ease of withdrawal of the tool shank from the tool socket.
The above and other objects, features, and advantages of this invention will become more apparent, and the invention itself will best be understood, from a study of the following description taken together with the attached drawings showing some preferred embodiments of the invention.